LED lamps, particularly retrofit LED lamps, are well known in the state of the art. A retrofit LED bulb can be perceived as a an LED lamp which can replace a common incandescent lamp or a halogen lamp or a compact fluorescent light without being adapted, that is having the same contacting base element (e.g. screwed contact base of an incandescent lamp, or pin contact elements of halogen lamps, or the like). The size of a retrofit LED light bulb is a serious limiting factor. The surface of the cooling element is competing with the light distributing element and the driving electronics. The larger the light diffuser the more an incandescent bulb radiation pattern is achieved. Feasible light transmissive materials have poor heat-conducting property, therefore the area used for light distribution is lost for heat transport to air.
A possible solution is heat convection by light transmissive fluids, having high temperature-density dependence. This problem has been addressed before in EP 1 881 259 A1, for instance, by immersing the LED module to a fluid bath. When doing so a high volume of the fluid is present having a high weight. Additionally, when heating up, the volume change is high, leading to a high overpressure inside the bulb such that the large quantity of hot liquid may spill when the light bulb got broken due to said overpressure.
Additionally, the cooling of LEDs in automotive headlamp applications is a challenge, and in most cases active cooling systems are used, wherein the other problem is the defrosting of the headlamp during cold seasons. Traditional headlamp sources (e.g. incandescent, halogen, discharge) radiate a significant portion of infrared light, thus defrosting the headlamp envelope.